1. Field of the Invention
This invention relates to improvements in a biocompatible ventricular assist and arrhythmia control device, as disclosed in U.S. patent application Ser. No. 07/019,701, now U.S. Pat. No. 4,925,443, and more particularly to a biocompatible ventricular assist and arrythmia control device comprising a gel-filled contact pad which forms part of a cardiac ventricular compression assembly, for compressing a heart ventricle without damaging the ventricle.
2. Description of the Prior Art
U.S patent application Ser. No. 07/019,701, filed Feb. 27, 1987, in the names of Marlin S. Heilman and Steve A. Kolenik, entitled "Biocompatible Ventricular Assist and Arrythmia Control Device", and assigned to the same Assignee as the subject application, discloses an implantable ventricular, assist device which includes (1) one or more movable compression assemblies for engaging the left ventricle of the heart; (2) an operating mechanism for cyclically actuating the movable compression assemblies and thereby alternately ejecting blood from the ventricle and permitting the ventricle to refill; (3) a sensing means to detect adequacy of left ventricular stroke volume and/or pressure; (4) a control mechanism to assure adequate left ventricular stroke volume by regulating the compressive force of the compression assemblies, and also to control pacemaker, cardioverter/defibrillator, and recorder subsystems; and (5) an electrical power source.
Each compression assembly includes a contoured pressure plate and a soft contact pad mounted on the interior plate surface for suturing and/or gluing the compression assembly to the ventricle. To minimize mechanical stress on the myocardial surface, including the coronary arteries, the contact pad consists of an elastomer, such as silicone rubber, or a thermoplastic material (Shore A durometer range 30-50). To avoid edge stress, the thickness of each contact pad is progressively reduced toward its periphery. To further reduce stresses on the myocardium, bearings and axles are used to mount the pressure plates on the compression assembly's driving arm; if the contracting heart produces a torquing force, the joint will permit the pressure plate, within specified limits, to follow the natural movement of the heart.
However, while the above ventricular assist device is considered to represent a significant advance over the prior art, it has been found that the edges of the compression assembly pressure plates tend to create pressure points which may cause possible damage to the heart, and that the amount of the heart encompassed by the compression assemblies may not be sufficient in all instances. Accordingly, one purpose of this invention is to improve the operation of the compression assembly and preclude any such damage, by replacing the contact pad of each compression assembly with a gel-filled contact pad of novel and advantageous construction, which can compress the heart ventricle uniformly without damaging the ventricle. Another purpose of the invention is to provide a ventricular assist device and associated compression assemblies which encompass a greater portion of the heart, and which also overcome the disadvantages of other known cardiac ventricular assist devices, such as those of the expandable and contractible balloon type, which tend to have a short operating life because of the excessive cyclical stretching required in their operation.